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Booleans

This is the simplest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

Syntax

To specify a boolean literal, use the keywords TRUE or FALSE. Both are case-insensitive.

<?php
$foo 
True// assign the value TRUE to $foo
?>

Typically, the result of an operator which returns a boolean value is passed on to a control structure.

<?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
    echo 
"The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo 
"<hr>\n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
    echo 
"<hr>\n";
}
?>

Converting to boolean

To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

  • the boolean FALSE itself
  • the integer 0 (zero)
  • the float 0.0 (zero)
  • the empty string, and the string "0"
  • an array with zero elements
  • an object with zero member variables (PHP 4 only)
  • the special type NULL (including unset variables)
  • SimpleXML objects created from empty tags

Every other value is considered TRUE (including any resource).

Warning

-1 is considered TRUE, like any other non-zero (whether negative or positive) number!

<?php
var_dump
((bool) "");        // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>

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